Disintigrate (6th level + quicken)
75 damage
Crown of stars (7th level)
26 per turn = 78 in a 3 round battle
Spiritual Weapon (7th level)
32 per turn = 96 in a 3 round battle
Firebolt + fire dragon sorc (convert a 7th level slot for 3 rounds of quicken + 1 SP).
21.5 per turn = 64.5 in 3 round
Sunbeam (6th level, AoE, concentration, action, half on miss)
27 per turn = 81 in 3 rounds.
All (except sunbeam) do nothing on a miss, so accuracy not included.
So unless you get multiple battles worth, something I find dubious even with an hour, I don't see it as all to great.
Your rationale for making Melf's minute meteors blue was that it does 50% more damage than fireball at 3rd level. Well, crown of stars does 370% more damage than fire storm at 7th level, 569% more than sunburst at 8th, and 104% more than meteor swarm at 9th. Unlike Melf's, it doesn't require concentration, and it lasts six times as long.
The net effect of crown of stars is to give you 7/9/11 quickened spells within the next hour, at the cost of 7/8/9 sorcery points instead of 14/18/22, while upgrading your fire bolt from 3/4d10 fire damage to 4d12 radiant. Accuracy should be a consideration, since not all save types (and AC) are equal, attacks can crit, and advantage on attacks is more common and cheaper than disadvantage on enemy saves. So:
Sunbeam: Con save, concentration, can't be scaled up, risk of friendly fire, and you're quickening anyway if you want to cast other spells.
Fire bolt + dragon bonus: I agree, crown of stars is better than fire bolts while quickening other spells, even for fire dragons. That makes it a whole lot better for the other 4.8 sorcerer subclasses.
Spiritual weapon: Double check the scaling. A 7th-level spiritual weapon does 3d8 + spellcasting mod. 18.5 * 3 = 55.5 damage. It's also not available to most sorcerers.
Quickened disintegrate: All right, and what are you doing with your action? Fire bolt? Twinned fire bolt? Well, if you had used your bonus action for crown of stars, you could cast a twinned disintegrate with your action. That's 176 damage with crown of stars, 108 without.
Beyond all that, at bottom I disagree with the calculation that you need to use it more than three times to get value. Crown of stars allows you to front-load damage and to use other spells with metamagic when you would otherwise be quickening them. It improves both damage per round and flow.
I also disagree about seeing more than one combat in an hour. In my experience, it is very common to fight, for example, undead minions in the first room, henchlings in the second, a stronger undead in the third, overseers in the fourth, and the boss in the fifth.
Most spells don't use advantage. And there's really no other feat that makes/breaks anything. Unless you have an odd score.
But fair point about wild. And shadow as well. So I'll add that one.
Greater invisibility + scorching ray should be in every sorcerer's playbook. Heck, dip two levels of hexblade warlock, cast eldritch blast and quickened scorching ray from invisibility with elven accuracy, and enjoy a 27.1% chance to crit on each attack.
Is crown of stars twinable?
Nope, but neither are any of the spells you just compared it to.